1. Technical Field
The present invention relates to a liquid discharge apparatus and a head unit.
2. Related Art
As an ink jet printer that discharges an ink and prints an image or a document, a printer that uses piezoelectric elements (for example, piezo elements) is known. The piezoelectric elements are provided respectively corresponding to a plurality of nozzles in a head unit and are respectively driven in response to drive signals and thereby, a predetermined amount of an ink (liquid) is discharged from the nozzle at a predetermined timing such that a dot is formed. The piezoelectric element is a capacitive load like a capacitor in terms of electric power. Therefore, a sufficient current supply is required to operate the piezoelectric elements of the nozzles.
Therefore, a configuration is employed, in which a drive signal amplified by using an amplifier circuit is supplied to a head unit such that the piezoelectric element is driven. Examples of the amplifier circuit include an amplifier circuit having a system (linear amplification, see JP-A-2009-190287) of performing current amplification of a source signal before amplification through class AB amplification or the like. However, since the linear amplification causes great power consumption and is poor in energy efficiency, class D amplification has been proposed (see JP-A-2010-114711).
Meanwhile, recently, there has been a strong demand for an ink jet printer in which high-speed printing or multiple tones are achieved. The high-speed printing can be realized by increasing the number of dots which can be formed per unit time. However, since one amplifier circuit can drive the limited number of piezoelectric elements (nozzles), many amplifier circuits are required.
In addition, multiple tones may be realized by increasing variations of an ink amount which is discharged from the nozzle. Therefore, a configuration is employed, in which one drive signal is selected from a plurality of types of drive signals prepared in advance in accordance with an ink amount to be discharged. Many amplifier circuits are also required for this configuration.
It is necessary to reduce a space to accommodate many amplifier circuits for miniaturization of the entire ink jet printer. Here, in order to achieve a high mounting density on the amplifier circuit, it is considered that a configuration (double-sided board mounting) is employed, in which elements of the amplifier circuit are mounted on both surfaces of a circuit board.
JP-A-2006-50431 discloses a method of arrangement of the elements of a class D amplifier circuit in the double-sided board mounting.
Incidentally, as described above, the high-speed printing can be realized by increasing the number of dots which can be formed per unit time and thus, a high ink-discharge frequency is required. Therefore, it is necessary to increase a switching frequency of class D amplification and to increase a frequency of the drive signal supplied to the piezoelectric element.
However, in a case where the drive signal has a high frequency, it has been pointed out that various problems such as an occurrence of noise will arise in the configuration in which the elements of the class D amplifier circuit are mounted on both surfaces of the circuit board.